GT380 Carb Issue

[barney01]

This is what i use https://www.ebay.co.uk/itm/Dual-Carbure ... Sw8oFXyhvU works great..

+1 Me too
https://youtu.be/9G5Hsenlv1g

[dreschr]

Alan- Yes your correct, I didn’t actually put a DTI through the plug opening to check for TDC, I just aligned the dot on the crank gear with the marker arrow and then fitted the cover/propeller ensuring the left cylinder mark on the propeller was aligned with the cast marking, as you advise this should put the piston at 3mm BTD. If both the middle and right cylinders run nicely wouldn’t that suggest the timing is correct?
Service Manual would be great, my email is dreschr@dreschr@karoo.co.uk
Before I open my wallet again for a carb rebuild (£380 for the last overhaul ) Ill give it another go, I will remove the carbs replace needles/jets etc and ensure they have had a good clean through and treat myself to the carb balancing kit as my other project is a CBX with 6 carbs!
Thanks for you advice Gents.
Regards
Rich

[yeadon_m]

Hi Rich,
I’ve owned a GT380B since 1978 & it’s my pride & joy! I’m on 2nd over & as this is a forever bike, I’ve collected some rare new old stock parts as I’ve gone along. A pair of outer exhausts isn’t quite the pinnacle, rare though they are. A full set of NOS 380A/B cylinders, anyone?
Anyhoo, to say i fiddled with this machine is an understatement & the one issue I’ve encountered often on aircooled Suzuki tripled yet never quite solved is, boom tish, challenges with left cylinder not running on choke. I’ve had two late model 380s & two late model 550s and all of them, to variable extents, suffer annoying unwillingness to run on choke, and always & only in the left cylinder.
I don’t understand why they did it but as you’ll have seen, the left carb has its own choke circuit but the centre & right share one choke circuit. If you peer into the carb intakes, you’ll see that the cross section of the left carb choke inlet is smaller than that in the centre carb, which delivers rich mixture to the centre but also the right cylinder via a rubber joining pipe on the engine side of the carb.
I often find the left cylinder on my 380 fires just for a few seconds when I kick it over, while the motor runs sweetly on centre & right. As soon as I knock the chokes closed, the left cylinder chines in az it should and all is well.
As I’ve never experienced the slightest issue starting this bike even after a whole winter standing in its shed, I’ve decided not to worry about why it’s odd on choke on the left.
But observation suggests it’s a rich mixture issue. Whether too much or too little, I’m not sure. I did briefly pursue the theory that, because the carb rod which lifts the slides wears more in its left bushing than right, it becomes impossible to super accurately set the closed throttles exactly the same. The extent of up and down wiggle in that left rod bushing (in the carb top turrets) is a good fraction of the tiny air gap between the throttle slide & carb body when the throttles are closed (normal cold start procedure) that the slide is too open or too closed to behave properly during choked running.
Against that, though, is the observation that the bike idles superbly on all pots as slowly as 1000rpm when hot.
I’ve had my carb top rebushed so I’ve no play, but I’ve also fitted a set of VM28s from a GT550 under that 380 carb top. It’s a great starter but even having done all these tweaks, left running on choke remains hit & miss and far inferior to centre & right pots.
One thing I tried was to disconnect the left choke lifted so it starts without choke on that pot only. It then did do cold starts evenly, suggesting it’s over choked by design.
If you ever solve this please do let me know. It’ll be obvious when someone cracks this, but until then, it’s a real head scratcher!
Good luck & enjoy,
Mike

[canaletto5]

I think the bikes were never designed to operate in a cold country

[Alan H]

Me three.....

[Harrymail]

Alan- Yes your correct, I didn’t actually put a DTI through the plug opening to check for TDC, I just aligned the dot on the crank gear with the marker arrow and then fitted the cover/propeller ensuring the left cylinder mark on the propeller was aligned with the cast marking, as you advise this should put the piston at 3mm BTD.
Regards
Rich

Rich, as Alan said, you shouldn't need to line the propeller up other than with the locating pin. The locating pin fixes its position. The pin is removable and easily gets lost. Is your locating pin present ?

Paul

[dreschr]

Hi Paul, yes I did fit the small pin so the propellar must be in the correct postion on the crank shaft, I guess when fitting the nylon drive gear it would be possible to get a "tooth out" during the installtion of the cover, but as i mentioned the middle and right cylinder sound great and run very smoothly so im presuming this is defiately a carb problem.

[Dbailey]

Hi... did you ever sort this? I have a left cylinder that won’t run properly. It fires on idle but not consistently. Looking at the plug it seems to be excess fuel. Carbs have been rebuilt with all new parts. I haven’t checked to see if I have a sticky choke valve. Thinking about it the lever got bent on the return from being refurbished. If the valve goes up and down with the fork can you assume the valve is operating as it should?

Thanks
Dave B

[Alan H]

Don't assume anything.
Who rebuilt the carbs, and with what exactly?

[barney01]

The choke piston has a rubber seal on the bottom. If it doesn't slide back to closed inrestricted its wont stop enriching.